Control means for a pair of fluid motors

ABSTRACT

A fluid pressure system comprising a pair of pilot actuated control valves, one of which has an inlet for pump output fluid and passage means through which the other is supplied with said pump fluid. Actuation of the valve element in said one control valve to a full operating position inhibits flow of pump output fluid to the other control valve until said valve element is returned at least partway toward its neutral position, and such partial return thereof is automatically effected as a consequence of actuation of the pilot for said other control valve.

United States Patent 1 91 [111 3,883,023 Bernhoft [451 May 13, 1975 [54]CONTROL MEANS FOR A PAIR OF FLUID 3,550,505 12/1970 Byers, Jr. 91/412MOTORS Inventor: Gerald W. Bernhoft, Wauwatosa,

Wis.

Koehring Company, Milwaukee, Wis.

Filed: June 12, 1972 Appl. No.: 262,024

Assignee:

US. Cl. 214/762; 91/412; 137/62563 Int. Cl E02f 3/32 Field of Search91/444, 448, 412, 411;

References Cited UNITED STATES PATENTS 5/1962 French 214/763 BUCKETCONTROL VALVE TILT Z1 STICK CONTROL VALVE Primary Examiner-Robert J.Spar Assistant Examiner-Ross Weaver Attorney, Agent, or Firm-James E.Nilles [57] ABSTRACT A fluid pressure system comprising a pair of pilotactuated control valves, one of which has an inlet for pump output fluidand passage means through which the other is supplied with said pumpfluid. Actuation of the valve element in said one control valve to afull operating position inhibits flow of pump output fluid to the othercontrol valve until said-valve element is returned at least partwaytoward its neutral position, and such partial return thereof isautomatically effected as a consequence of actuation of the pilot forsaid other control valve.

5 Claims, 2 Drawing Figures EXTEND PATENTEB 31975 sum 1 a? 2 F GE SHEET2 OF 2 TILT 72.

PATENTED RAY I 31975 6 J 26 32 Ml 1 l BUCKET CONTROL VALVE STICK CONTROLVALVE l\/ CONTROL MEANS FOR A PAIR OF FLUID MOTORS BACKGROUND OF THEINVENTION This invention relates to fluid pressure systems in which apair of liquid motors must at times be operated simultaneously, inconsequence of actuation of pressure compensated control valvestherefor.

As is well known, when two such pressure compensated control valves areconnected together in a bank having a common inlet or supply passage forpump output fluid, that valve which is closer to the inlet has priorityover the other. This is to say that if the valve element or spool of thefirst control valve is in a full operating position, all of the pumpoutput fluid entering the inlet would flow to the fluid motor governedby said first valve, and none would be available for operation of themotor governed by the second control valve. In that case, only one ofthe fluid motors could be operated at a time.

A hydraulically operated backhoe is but one example of a mechanismhaving two fluid motors, in this case double acting hydraulic cylinders,which frequently must be operated concurrently in order to efficientlyperform its digging function. A first pressure compensated valve can beone which controls the bucket cylinder, and the second pressurecompensated valve can be one which controls the stick cylinder. If thebucket control valve is nearer the inlet and is actuated to a.fulloperating position, all of the pump flow is directed into the bucketcylinder, and operation of the stick cylinder is impossible.

Inasmuch as all control valves have a maximum capacity, one solution tothe aforementioned problem would be to supply a volume of pressure fluidto the inlet of the valve bank in excess of the capacity of the firstvalve section. In this way, sufficient fluid could be made available forsimultaneous operation of both the bucket and stick cylinders. Thissolution, however, is subject to the objection that additionalhorsepower would be required, which additional horsepower would bewasted when only one of the cylinders was in operation.

Another solution to the problem involves practice of an expedient whichhas for long been quite common to operators of parallel and/orseries-parallel control valves. This expedient required the operator tomanually return the valve element of the first control valve partwaytoward its neutral position, in order to divert some of the incomingpump fluid to the motor governed by the second control valve. Forsimultaneous operation of the bucket and the stick cylinders of abackhoe, therefore, the operator had to acquire a certain degree ofskill in the manual manipulation of the hand levers on their respectivecontrol valves and he frequently had to hunt for the proper positions ofboth valve elements, by continuously shifting their levers back andforth to obtain the desired rates of fluid flow to the motors governedby the control valves.

SUMMARY OF THE INVENTION It is the purpose of the present invention toprovide a fluid pressure system comprising a plural spool pilot operatedcontrol valve mechanism having a common pressure fluid supply passagefor said spools, and wherein instrumentalities incorporated in thesystem function automatically to effect partial retraction from a fulloperating position of the valve element of a first control valve nearestthe inlet of the supply passage, as a consequence of actuation of thevalve element of a second control valve downstream from the first in thedirection of fluid flow through the supply passage, to thereby makepressure fluid available to the service passages governed by the secondcontrol valve.

More specifically it is an object of the invention to provide a controlvalve mechanism comprising a pair of pilot operated control valves,wherein actuation of the pilot to effect shifting of one control spoolto an operating position automatically effects retraction of the controlspool nearer the inlet of the mechanism from a full flow operatingposition thereof partway toward a neutral position to thus enable flowof inlet fluid to service passage means governed by the downstream valvespool.

With these observations and objectives in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings, which exemplify theinvention, it being understood that changes may be made in the specificapparatus disclosed herein without departing from the essentials of theinvention set forth in the appended claims.

The accompanying drawings illustrate one complete example of anembodiment of the invention constructed according to the best mode sofar devised for the practical application of the principles thereof, andin which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of amaterial handling device, such as a backhoe embodying this invention,and

' FIG. 2 is a graphic diagram of a fluid pressure system employed incarrying out the invention.

DETAILED DESCRIPTION The invention is embodied in a material handlingdevice, such as a backhoe illustrated in FIG. 1, and including a boom 1to which an arm or stick 2 is pivoted for relative movement. Inaddition, a tool,such as a bucket 3, is pivoted to the arm 2 forrelative pivotal movement. A hydraulic cylinder A is connected betweenthe tool 3 and the stick 2 which upon extension of the hydrauliccylinder A causes clockwise pivotal movement of the bucket 3 relative tothe arm 2. A similar cylinder B is connected between the arm 2 and theboom 1 which acts as a support so that extension of the hydrauliccylinder B causes the stick 2 to pivot in a clockwise direction relativeto the boom 1.

Referring now more particularly to FIG. 2, it will be seen that thesystem comprises a control valve mechanism 4 having a pressure fluidinlet 5, an outlet 6, and first and second control valves 7 and 8 whichcan comprise two juxtaposed sections of a bank whose inlet 5 is suppliedwith pressure fluid from the output port of a pump 9. The first controlvalve 7 is that which is nearer the inlet 5 and can be considered as theupstream valve for controlling the cylinder A in FIG. 1. The secondcontrol valve 8 can thus be referred to as the second or downstreamvalve for controlling the cylinder B. The valve 7 is connected byhydraulic lines 711 and 7b to the opposite ends of hydraulic cylinder Aand valve 8 is connected by hydraulic lines 8a and 8b to the oppositeends of hydraulic cylinder B.

Each of the control valves has been shown as of the pressure compensatedtype having a control spool which is movable out of its neutral positionindicated in the diagram to operating positions at opposite sides ofneutral. Fluid pressure operated actuators 10, one connected with eachend of each spool, provides for shifting of the spools to one or theother of their respective operating positions at the dictate of pilotvalves such as generally designated 11. While each actuator 10 has itsown pilot valve 11, only two have been shown in the diagram, one for theactuator 10 at the left hand end of the upstream control valve 7, andone for the actuator 10 at the right hand end of the downstream controlvalve 8.

All of the pilot valves are connected with a common source of pilotfluid under pressure. For purposes of illustration the pilot fluid cancomprise air under pressure brought in to the system through a duct 12.The pilot valves 11 are of the type disclosed in detail in the copendingapplication of Gerald W. Bernhoft and David A. Miller Ser. No. 195,581,filed Nov. 4, 1971 and entitled Control For Mobile Construction Machinenow US. Pat. 3,773,084, granted Nov. 20, 1973. In fact, the pilotcircuitry herein shown follows to a considerable extent that which isdisclosed in said copending application.

Each pilot valve 11 has a plunger which is movable up and down isnormally held in a closed upper position blocking flow of air underpressure from the air line 12 to the actuators l0. Depression of theplunger of the pilot 11 for control valve 7 effects shifting of thespool thereof to a full operating position to the right of neutral bythe actuator 10 at its left hand end; while depression of the plunger ofthe pilot 11 for control valve 8 effects shifting of its spool to a fulloperating position to the left of neutral by the actuator 10 at itsright hand end.

With pressure compensated control valves like those graphically shown inthe diagram, pressure fluid entering the inlet from the pump 9 is ableto flow substantially freely through a common supply passage such asindicated at 14 as long as the spools of both control valves remain intheir neutral positions shown. Each one of the valves, when actuatedseparately to a full operating position at the dictate of its pilot 11,is capable of directing substantially the entire output of the pump 9 tothe hydraulic cylinder A or B governed thereby.

However, as is the case with series-parallel valves, if the spool of thefirst or upstream control valve 7 is in a full operating position, itinhibits flow of supply fluid to the second or downstream control valve8. As a result, the cylinder governed by the downstream control valve 8cannot be operated until the spool of the upstream control valve 7 isreturned to neutral, or at least partway toward neutral to a positionmetering flow to its associated cylinder and thereby allowing some ofthe pump output fluid entering the inlet 5 to flow to the downstreamcontrol valve 8 for operation of the cylinder governed therebyconcurrently with the cylinder governed by the upstream control valve 7.

As explained in the aforesaid copending application, however, it ispossible by manual regulation of the position of the plunger of pilotvalve 11 for control valve 7 to place it in any one of a number ofundefined positions intermediate its closed and fully open positions,

to effect reduction of the air pressure in the associated actuator to avalue at which the force it exerts on the spool of valve 7 balances theforce of the return spring 15 thereon at some metering position of thespool between its neutral and full fiow positions. In this way part ofthe pump fluid entering the inlet 5 can flow to the cylinder governed bycontrol valve 7 and the remainder can be made to flow to the cylindergoverned by control valve 8.

According to this invention the operator of apparatus, such as abackhoe, having the fluid pressure system herein illustrated, does nothave to hunt for intermediate position the plunger of pilot 11 for valve7 must occupy in order to enable concurrent operation of the cylindersgoverned by the control valves 7 and 8. For example, one of thesecylinders can be that which governs the tilting and dumping motions ofthe bucket under the control of the upstream valve 7, and the othercylinder can be that which is governed by the downstream control valve 8and effects the dig and extend motions of the stick upon which thebucket is mounted.

If it is assumed that the plunger is held in a fully depressed positionin the pilot 11 for the upstream control valve 7, so that the spoolthereof will accordingly be in a full flow bucket tilt position at whichall of the pump output fluid entering the inlet 5 flows to the bucketcylinder, the operator can automatically effect partial retraction ofsaid spool and operation of the stick cylinder to cause digging motionof the stick concurrently with tilting motion of the bucket merely byactuation of the pilot 11 for the right hand actuator 10 of thedownstream control valve 8.

A full discussion of the pilot circuitry which follows, is necessary toan understanding of how this desired concurrent operation of thecylinders governed by both control valves is achieved without anyrepositioning of the plunger in the pilot for the bucket control valve7.

The pilot circuit for the actuator 10 at the left hand end of the bucketcontrol valve 7 will be first described. Air under pressure of about psiin line 12 enters a reducing valve 17 and flows therefrom to the inletof pilot 11 via a duct 18 at a pressure of about 35 psi. An outlet duct19 leads from the pilot valve and is connected with an amplifier 20 of acommercially available type manufactured by the Bellofram Corp. andknown as its Model 362 relay.

The pressure in the duct 19 can be anywhere from 5 to 35 psi, dependingupon the extent to which the plunger of the pilot valve 11 has beendepressed. This pressure is controlled by bypassing incoming air to theatmosphere in an amount which decreases with downward motion of thepilot plunger until its fully open position is reached at the end of theplunger stroke.

Depending upon the pressure of the air entering the relay or amplifier20, the pressure of the air flowing into a duct 21 from the outlet ofthe relay will vary from about 15 to 90 psi. For the purposes of thisinvention the duct 21 can be considered as a fluid pressure supply linefor the actuator 10 at the left hand end of the bucket control valve 7.i

If only that pilot valve governing bucket tilt is actuated to a fullflow position, pilot fluid (air) in the supply duct 21 normally flowsthrough the left hand section 22 of a two position three port valveinstrumentality 23 to a duct 24 connecting with the valve actuator 10,to subject the same to the full pressure of pilot fluid in duct 21.This, of course, effects shifting of the spool in the bucket controlvalve 7 to a full operating position to the right of neutral, againstthe force of its return spring 15.

The two position valve instrumentality 23 is biased to the positiondescribed above by a spring 25. It is also provided with a fluidpressure actuator 26 in the form of an air cylinder which, whenconnected with a source of air under pressure, effects shifting of saidvalve instrumentality to its other position to communicate the duct 24with a duct 26 forming a branch of the supply duct 21.

An adjustable pressure regulating valve 27 in branch 28 of the supplyduct is normally set to reduce the pressure of pilot fluid flowing tothe actuator 10 through the valve instrumentality 23 to a value such asto allow the spring to retract the spool of the bucket control valve 7partway toward neutral, to a position at which the fluid pressure forceexerted on the spool by the left hand actuator 10 balances the returnforce exerted on the spool by the spring 15.

By way of example, with a spring 15 of given strength, and with thepressure of pilot fluid in the supply duct 21 at a maximum value ofabout 90 psi, and assuming that the valve instrumentality 23 has beenactuated to its position routing pilot fluid to the actuator duct 24through the pressure regulating valve 27, the pressure of fluid thenentering duct 24 will be about 52 psi. In other words, the opposingforces of spring pressure on one end of the bucket spool and of pilotactuator pressure on the other end of the spool will hold the spool in ametering position such as to make pump fluid available to the spool ofthe stick cylinder 8.-

It should be noted that the pressure regulating valve 27 is of the selfrelieving type so as to dissipate any of the higher pressure air fromthe actuator 10 when the valve instrumentality 23 is shifted to its lastdescribed position.

It should also be understood that a duplicate of the pilot valve 11 andpilot circuitry described is provided for the actuator 10 at the righthand end of the bucket control valve 7, to govern dump.

The valve instrumentality 23 will be shifted to its position routingpilot fluid through the pressure regulating valve 27 as a consequence ofactuation of the pilot valve 11 for either actuator 10 of the stickcontrol valve 8. The pilot circuitry for each actuator 10 of the stickcontrol valve is the same as that described except that the pressureregulating valve 27 and fluid pressure actuated valve instrumentality 23are eliminated therefrom.

For convenience, only that pilot valve 11 and pilot circuitry whichcontrols the actuator 10 for the dig function of the stick control valvehas been illustrated. Manual depression of the plunger of the pilotvalve 11 for dig brings fluid (air) under pressure into the pilot supplyduct 121. This duct leads to the actuator 10 at the right hand end ofthe stick control valve and it also has a branch 30 which leads througha shuttle valve 31 to a control duct 32 connecting with the fluidpressure actuator 26 for the two position valve instrumentality 23.

Accordingly, if the bucket control spool is in its full flow tiltposition directing the entire pump output to the bucket cylinder at thetime the plunger of the pilot valve 11 is depressed to effect actuationof the stick control valve for the dig function, the resultingpressurization of duct 121 with pilot fluid will effect actuation of thevalve instrumentality 23 and disconnection of the actuator 10 for thebucket control valve from its supply duct 21, and pilot fluid will berouted to said actuator at reduced pressure through the regulator 27 andthe two position valve instrumentality 23.

The spool of the bucket control valve 7 then assumes an intermediate ormetering position at which part of the pump fluid entering the inlet 5of the control valve mechanism is directed to the bucket cylinder andthe remainder is directed to the stick cylinder. In this way, the bucketand stick cylinders can be operated simultaneously, to effect thedesired digging action through the combined tilt and dig movement of thebucket and stick, respectively.

From this it will be seen that the adjustment of the pressure regulatingvalve 27 will determine how much pump output fluid will be diverted tothe stick cylinder with a return spring 15 of given strength acting uponthe spool of the upstream control valve 7.

The same retracting motion of the spool in the bucket control valvetakes place upon depression of the plunger in the pilot valve (notshown) for the actuator 10 at the left hand end of the stick controlvalve. In that event, the actuator 26 for the two position valveinstrumentality is again pressurized by pilot fluid (air) under pressurein the actuator supply duct 221 through a branch 35 connecting it withthe actuator through the shuttle valve 31 and the duct 32.

From the foregoing description, together with the accompanying drawing,it will be readily apparent to those skilled in the art that thisinvention provides a fluid pressure system which automatically providesfor partial retraction of the spool of a first pilot operated controlvalve from a full flow position, to enable simultaneous operation of twofluid motors, as a consequence of actuation of a pilot valve for asecond control valve; and that adjustable instrumentalities incorporatedin the system provide for such simultaneous operation of the fluidmotors at optimum speeds without the necessity for repositioning oftheir pilot valves during such operation.

It will be further apparent that this invention is applicable to pilotoperated control valve system regardless of whether the pilot valves andcircuits governed thereby employ air or hydraulic fluid; and that thepilot valves themselves can be solenoid operated in some installationswhere remote control of the pilot valves is desired.

Those skilled in the art will appreciate that the invention can beembodied in forms other than as herein disclosed for purposes ofillustration.

The invention is defined by the following claims:

1. In a material handling device including a pivotally mounted arm, atool pivotally mounted on the arm, first and second fluid motor meansfor independently pivotally moving the arm and the tool, respectively,pump means for directing fluid to the first and second motor means,first valve means movable from a closed to an open position fordirecting fluid from said pump means to one of said first and secondmotor means, second valve means movable from a closed to an openposition for directing fluid from said pump means to the other of saidfirst and second motor means and manual actuator means for each of saidfirst and second valve means; the improvement comprising: control means,including a separate source of fluid pressure and pressure operatedmeans communicating with said separate source for moving said first andsecond valve means between open and closed positions, operativelyconnected between said first and second valve means for moving saidfirst valve means to a partially closed position in response to openingof said second valve means whereby said arm and said tool are pivotedsimultaneously at a reduced speed. v

2. In a material handling device including a pivotally mounted arm, atool pivotally mounted on the arm, separate fluid motors for pivotallymoving the arm and the tool, pump means providing a pressure fluidsource for operation of said motors, a first control valve actuatablefrom a closed to an open position to direct pressure fluid from saidsource to one of said motors, a second control valve actuatable from aclosed to a fully open position to direct pressure fluid from saidsource to the other motor and in which said first control valve in itsfully open ,position precludes flow of pressure fluid from the source tosaid second control valve, the improvement which comprises:

A. manually operated actuator means for each of said first and secondcontrol valves for effecting such actuation thereof;

B. and control means connected with said first and second control valvesand with the actuator means for said first control valve andoperablewhenever said first control valve is in its fully open position, and inconsequence of valve opening operation of the actuator means for saidsecond control valve,

- to effect movement of said first control valve to a partially closedposition without necessitating manual adjustment of the actuator meansfor said first control valve, to thereby effect diversion of pressurefluid from the source to the motor governed by said second control valvefor concurrent and independent pivotal motion of the arm and tool, saidcontrol means comprising a separate source of control pressure, and saidmanually operated actuator means including pressure responsive means foreach of said first and second control valves communicating with saidsource of control pressure for moving said valves from said closed toopen positions in response to pressure from said separate source.

3. A material handling device comprising, a support, an arm pivoted tosaid support, a tool pivoted to said arm, a first fluid motor operableto pivot said arm relative to said support, a second fluid motoroperable to pivot said tool relative to said arm, pump means providing apressure fluid source for operation of said motors, a first valve meansmovable between closed and open positions to control fluid flow fromsaid source to said first motor, a second control valve means movablebetween closed and open positions to control fluid flow from said sourceto said second motor, a separate source of fluid pressure, pressureoperated means communicating with said separate source for moving saidcontrol valve means between open and closed positions, control meansoperatively connected to said pressure operated means for moving saidfirst valve means from said open towards said closed positions inresponse to movement of said second valve means from said closed to saidopen position for simultaneous and independent operation of said firstand second motors.

4. A material handling device comprising, a support, an arm pivoted tosaid support, a tool pivoted to said arm, a first fluid motor operableto pivot said arm relative to said support, a second fluid motoroperable to pivot said tool relative to said arm, pump means providing apressure fluid source for operation of said motors, first and secondvalve means, said first valve means being movable between first andsecond positions to control fluid flow from said source to said firstmotor and to said second valve means, said second valve means beingmovable between first and second positions to control fluid flow fromsaid source to said second fluid motor, said second valve means beingsubstantially isolated from said pressure fluid source when said firstvalve means is in said second position, a separate source of fluid, afirst pressure operated means operatively connected to said first valvemeans and a second pressure operated means operatively connected to saidsecond valve means for moving each of said valve means between saidfirst and second positions, first and second manually movable controlvalves disposed between said separate source and said first and secondpressure operated means, respectively, and being operative to controldelivery of pressure to said pressure operated means, and control meansoperatively connected between said first and second pressure operatedmeans for moving said first valve means'from said second towards saidfirst position in response to pressure in said second pressure operatedmeans for simultaneous delivery of fluid from said source to said firstand second valve means for independent and simultaneous operation ofsaid first and second fluid motors.

5. The combination of claim 4 in which said control means includes apressure controlling valve connected to said first pressure operatedmeans and to said separate source of pressure, said pressure controllingvalve being operative in response to pressure in said second pressureoperating means to reduce the pressure in said first pressure operatingmeans for movement of said first valve means from said second towardssaid first position of the latter for communicating said second valvemeans with said first valve means for said simultaneous and independentpivotal movement of said arm and said tool.

1. In a material handling device including a pivotally mounted arm, atool pivotally mounted on the arm, first and second fluid motor meansfor independently pivotally moving the arm and the tool, respectively,pump means for directing fluid to the first and second motor means,first valve means movable from a closed to an open position fordirecting fluid from said pump means to one of said first and secondmotor means, second valve means movable from a closed to an openposition for directing fluid from said pump means to the other of saidfirst and second motor means and manual actuator means for each of saidfirst and second valve means; the improvement comprising: control means,including a separate source of fluid pressure and pressure operatedmeans communicating with said separate source for moving said first andsecond valve means between open and closed positions, operativelyconnected between said first and second valve means for moving saidfirst valve means to a partially closed position in response to openingof said second valve means whereby said arm and said tool are pivotedsimultaneously at a reduced speed.
 2. In a material handling deviceincluding a pivotally mounted arm, a tool pivotally mounted on the arm,separate fluid motors for pivotally moving the arm and the tool, pumpmeans providing a pressure fluid source for operation of said motors, afirst control valve actuatable from a closed to an open position todirect pressure fluid from said source to one of said motors, a secondcontrol valve actuatable from a closed to a fully open position todirect pressure fluid from said source to the other motor and in whichsaid first control valve in its fully open position precludes flow ofpressure fluid from the source to said second control valve, theimprovement which comprises: A. manually operated actuator means foreach of said first and second control valves for effecting suchactuation thereof; B. and control means connected with said first andsecond control valves and with the actuator means for said first controlvalve and operable whenever said first control valve is in its fullyopen position, and in consequence of valve opening operation of theactuator means for said second control valve, to effect movement of saidfirst control valve to a partially closed position without necessitatingmanual adjustment of the actuator means for said first control valve, tothereby effect diversion of pressure fluid from the source to the motorgoverned by said second control valve for concurrent and independentpivotal motion of the arm and tool, said control means comprising aseparate source of control pressure, and said manually operated actuatormeans including pressure responsive means for each of said first andsecond control valves communicating with said source of control pressurefor moving said valves from said closed to open positions in response topressure from said separate source.
 3. A material handling devicecomprising, a support, an arm pivoted to said support, a tool pivoted tosaid arm, a first fluid motor operable to pivot said arm relative tosaid support, a second fluid motor operable to pivot said tool rElativeto said arm, pump means providing a pressure fluid source for operationof said motors, a first valve means movable between closed and openpositions to control fluid flow from said source to said first motor, asecond control valve means movable between closed and open positions tocontrol fluid flow from said source to said second motor, a separatesource of fluid pressure, pressure operated means communicating withsaid separate source for moving said control valve means between openand closed positions, control means operatively connected to saidpressure operated means for moving said first valve means from said opentowards said closed positions in response to movement of said secondvalve means from said closed to said open position for simultaneous andindependent operation of said first and second motors.
 4. A materialhandling device comprising, a support, an arm pivoted to said support, atool pivoted to said arm, a first fluid motor operable to pivot said armrelative to said support, a second fluid motor operable to pivot saidtool relative to said arm, pump means providing a pressure fluid sourcefor operation of said motors, first and second valve means, said firstvalve means being movable between first and second positions to controlfluid flow from said source to said first motor and to said second valvemeans, said second valve means being movable between first and secondpositions to control fluid flow from said source to said second fluidmotor, said second valve means being substantially isolated from saidpressure fluid source when said first valve means is in said secondposition, a separate source of fluid, a first pressure operated meansoperatively connected to said first valve means and a second pressureoperated means operatively connected to said second valve means formoving each of said valve means between said first and second positions,first and second manually movable control valves disposed between saidseparate source and said first and second pressure operated means,respectively, and being operative to control delivery of pressure tosaid pressure operated means, and control means operatively connectedbetween said first and second pressure operated means for moving saidfirst valve means from said second towards said first position inresponse to pressure in said second pressure operated means forsimultaneous delivery of fluid from said source to said first and secondvalve means for independent and simultaneous operation of said first andsecond fluid motors.
 5. The combination of claim 4 in which said controlmeans includes a pressure controlling valve connected to said firstpressure operated means and to said separate source of pressure, saidpressure controlling valve being operative in response to pressure insaid second pressure operating means to reduce the pressure in saidfirst pressure operating means for movement of said first valve meansfrom said second towards said first position of the latter forcommunicating said second valve means with said first valve means forsaid simultaneous and independent pivotal movement of said arm and saidtool.